1. Field of the Invention
This disclosure is directed to a copy protection and scrambling method and apparatus for use with various video platforms including, but not limited to: (1) digital video recording, where it is desired to copy protect both an analog and digital video signal associated with a digital recording or playback apparatus; (2) a digital pay per view decoder where it is desired to copy protect a digital video signal received by the decoder; and (3) a digital video disc player, where it is desired to copy protect the digital video signal associated with a digital disk recording. Additionally, the elements of the copy protection and scrambling can be applied to any video material where the original source material is not copy protected;
2. Description of the Prior Art
Progressive improvements in recording head technology, high-speed digital signal processing and videotape formulation now make it feasible to manufacture digital VCRs for consumer applications. A coalition of manufacturers has been convened specifically to promulgate technical standards for digital VCRs for consumer use. A similar effort appears to be under way on a new MPEG-2 digital video disc standard--DVD.
The success of the digital VCR as a consumer product will be decisively influenced by video software suppliers' decisions to support it by releasing movies and other quality programming in the format. The extremely high picture quality potential of digital VCRs coupled with their ability to make endless perfect copies, represent a serious psychological obstacle to many program suppliers, especially the Hollywood studios. As digital VCRs get into the hands of professional and amateur pirates they will be viewed as a major threat to revenues.
To encourage program suppliers to view digital VCRs as an opportunity rather than a threat, a sophisticated copyright protection system that provides a high level of security for certain copyrighted video programs is needed. This needs to be accomplished without in any way compromising the consumers' ability to use these digital VCRs for legitimate time-shifting and prerecorded program viewing.
Overview of Video Cody-Protection Systems
The various video copy-protection systems implemented or proposed to date have in one way or another attempted to prevent VCRs from making usable copies of certain pre-recorded or transmitted video programs. There are two general classes of such systems--called respectively, unilateral and bilateral copy-protection systems.
Unilateral copy-protection systems: as described in U.S. Pat. No. 4,631,603 issued Dec. 23, 1986, to John O. Ryan and assigned to Macrovision; U.S. Pat. No. 4,914,694 issued on Apr. 3, 1990 to Leonard and assigned to Eidak Corp.; and U.S. Pat. No. 4,577,216 issued Mar. 18, 1986, to John O. Ryan and assigned to Macrovision; are systems designed to work with large pre-existing installed bases of VCRs and TV sets. The designer of a unilateral system must identify and exploit some basic difference between the way these pre-existing VCRs and TV sets utilize the video signal. Since the pre-existing VCRs were designed to be able to record all video signals conforming to the standard in use (e.g. NTSC or PAL), unilateral copy-protection systems therefore must generate non-standard video signals. The requirement that these non-standard copy-protected video signals be playable on all existing VCRs and TV sets places such severe design constraints on unilateral systems that a level of effectiveness much above about 80% is very difficult to achieve.
Various well known copy protection schemes for video signals include that disclosed in U.S. Pat. No. 4,631,603, John O. Ryan, Dec. 23, 1986 and assigned to Macrovision, incorporated by reference, directed to modifying an analog video signal to inhibit making of acceptable video recordings therefrom. This discloses adding a plurality of pulse pairs to the otherwise unused lines of a video signal vertical blanking interval, each pulse pair being a negative-going pulse followed closely by a positive-going pulse. The effect is to confuse AGC (automatic gain control circuitry) of a VCR (video cassette recorder) recording such a signal, so that the recorded signal is of poor quality and generally unview able.
Another analog video protection scheme is disclosed in U.S. Pat. No. 4,914,694 issued Apr. 3, 1990, to Leonard, and assigned to Eidak Corp., incorporated by reference. The Eidak system (see Abstract) increases or decreases the length of each video field from the standard length, either by changing the time duration of the respective horizontal line intervals in each field while keeping a constant, standard number of lines per frame, or by changing the number of horizontal line intervals which constitute a frame while maintaining the standard duration of each line interval.
These video protection systems modify the video signal to be recorded (for instance on tape) or to be broadcast (for instance pay-per-view television programs) to make copying by ordinary VCRs difficult or impossible. When a video tape, on which is recorded the copy protected video signal, is played back for viewing using a VCR, the copy protection process is essentially transparent, i.e., it does not interfere with viewing. However, any attempt made to copy the video signal from the tape using a second VCR to record the output of the first (playback) VCR yields a picture degraded to some extent, depending on the efficacy of the particular copy protection system. These present video copy protection systems protect only analog video signals which are the type of video signals broadcast and recorded using current consumer video technology.
Bilateral copy-protection systems, on the other hand, require that a special detector circuit be included in essentially all VCRs conforming to the standard. Bilateral systems therefore represent a viable alternative to unilateral systems only if they are implemented at the introduction of a new format. This detector circuit searches for a special copy-disable signal embedded in protected pre-recorded or transmitted video signals and on finding it, causes the VCR to stop recording. Bilateral copy-protection systems can be designed to be essentially 100% effective. For this reason they are preferred by copyright owners over unilateral systems.
However for a bilateral system to have maximum value, it must be designed in as an integral part of a new VCR format and the special detector circuit must be included in all manufactured VCRs. There may be legal or contractual difficulties in ensuring the cooperation of all VCR manufacturers. If non-compliant VCRs are manufactured, these surely will be purchased by some video store owners and professional video pirates, and will be used to make illicit copies of protected programs to be sold or rented. This necessity of ensuring the cooperation of 100% of VCR manufacturers is a weakness of all bilateral copy-protection systems proposed to date.
Future of Digital Recording
It is widely believed that digital video tape recorders will soon be commercially available for consumer use. To maintain compatibility with analog video broadcast signals and analog video tape recorders, it is likely that at least the first generation of consumer digital video tape recorders will be "hybrid" digital and analog systems. Such systems will have the capabilities of current analog video cassette recorders to record from an analog input signal and provide an analog output signal on playback, while still having equivalent digital capabilities. Thus these new hybrid digital tape recorders will have the capability internally to convert input analog signals into digital signals, and record the digital signals as a digital data stream on the tape. During playback the digital data stream from the tape will be available both as a digital signal for display by a digital television set (also not currently available) or be reconverted within the hybrid video tape recorder to a conventional analog video signal (such as the NTSC signal used in the United States.) The capability of the system internally to convert the received analog signals to a digital data stream will be important because currently there are no sources (either tape or broadcast) of digital video program material available to consumers.
Such hybrid video recorders will likely employ a "consumer" digital recording format differing from the standards of present professional digital systems. This consumer digital video format is not yet established. Such digital video recorders will likely include a conventional "front end" RF tuner and also an RF modulator on the output side, as do present conventional analog VCRs. (By analog video here is meant NTSC, PAL, SECAM or Y/C.) The digital recording standard for consumers is likely to be essentially a data structure that represents the video signal as a stream of (binary) data bits along with suitable error concealment encoding, together with a physical tape standard.
Also well known are professional digital video tape recorders, although currently such digital video tape recorders (which both record and play back digitally) are available only for the professional market, due to their high cost. Such digital systems trade distortion-free performance for substantially higher bandwidth, i.e. substantially more information must be recorded per video frame. The advantage to the user of a digital recorder is that so long as the signals are recorded and played back in the digital domain, each successive generation of copies is without any significant reduction in picture quality. This is unlike the case with conventional analog recording technology. Current digital video recorders (not intended for consumer purposes) a use the so-called "D-1", "D-2" or "D-3" video recording standards and require special video tape.
Problems Posed by Digital Recording
Since digital video tape recorders will be capable of high fidelity reproduction which in turn will encourage copying, it is important that such recorders for consumer use be designed to inhibit or discourage unauthorized recording. For instance it is important to prevent use of recorders for illegally duplicating copyrighted video material, and also to prevent playing back of such illegally duplicated material. Currently available analog video copy protection techniques are not useful in the digital domain. Hence there is a need for a new copy protection system suitable for use with such hybrid digital and analog video tape recorders, where the material recorded on the tape is a digital data stream. A typical situation to be prevented is use of a hybrid video tape recorder to copy an output signal from a conventional VHS VCR, where the tape played back from the VHS VCR has a conventional copy protection process applied to it. The problem is to prevent the new hybrid digital-analog video tape recorder from copying the material from such a tape. Otherwise, the existence of such hybrid recorders would encourage copyright infringement.
Some of the problems cited above were solved by U.S. Pat. No. 5,315,448, issued May 24, 1994, issued to Ryan and assigned to Macrovision Corporation, incorporated by reference.
The Problem
The digital VCR represents a potential threat to video copyright owners in three ways:
1. Its ability to make high-quality copies of existing analog video programs (NTSC or PAL), whether from pre-recorded videocassettes, laser discs or cable PPV decoders. PA1 2. Its ability to perfectly replicate pre-recorded digital videocassette or make perfect copies of digital video programs from future DVD players, or from PPV decoders with digital video outputs. PA1 3. Its ability to provide near studio-quality analog video outputs from digital pre-recorded videocassettes, which can therefore be copied by existing VHS and 8 mm VCRs. The quality of these analog copies will be comparable to that of today's original VHS releases.